Abstract:

A marine vessel propulsion system includes multiple propulsion devices,
multiple operation levers, and multiple lever position sensors arranged
to detect the positions of the multiple operation levers, and a control
unit. The control unit is programmed to control, based on detection
results from the multiple lever position sensors, the shift states of the
respective propulsion devices and to change the steering angle of at
least one of the propulsion devices. The control unit may be arranged to
change the steering angles of the propulsion devices to facilitate the
behavior of the hull corresponding to the shift states of the respective
propulsion devices.

Claims:

1. A marine vessel propulsion system comprising:a plurality of propulsion
devices arranged to be mounted on a hull so as to enable a steering angle
to change;a plurality of operation levers arranged to be operated by a
marine vessel maneuvering operator to control the plurality of propulsion
devices to change respective shift states selected from among a forward
drive state, a neutral state, and a reverse drive state;a plurality of
lever position sensors provided correspondingly to the plurality of
respective operation levers and arranged to detect positions of the
operation levers; anda control unit programmed to control, based on
detection results from the plurality of lever position sensors, the shift
states of the respective propulsion devices and to change the steering
angle of at least one of the propulsion devices to facilitate a behavior
of the hull corresponding to the shift states of the respective
propulsion devices.

2. The marine vessel propulsion system according to claim 1, wherein the
control unit is programmed to control the shift states of the plurality
of respective propulsion devices based on detection results from the
plurality of lever position sensors such that the positions of the
operation levers correspond to the shift states of the respective
propulsion devices.

3. The marine vessel propulsion system according to claim 2, whereinthe
plurality of propulsion devices include a first propulsion device group
including at least one of the propulsion devices and a second propulsion
device group including at least one of the propulsion devices not
included in the first propulsion device group;the plurality of operation
levers include a first operation lever corresponding to the first
propulsion device group and a second operation lever corresponding to the
second propulsion device group;the control unit is programmed to change,
when a position of the first operation lever is different from a position
of the second operation lever, the steering angle of at least one of the
propulsion devices to facilitate the behavior of the hull corresponding
to shift states of the respective first and second propulsion device
groups.

4. The marine vessel propulsion system according to claim 3, whereinthe
first and second operation levers are arranged to be movable among a
forward drive position corresponding to the forward drive state, a
neutral position corresponding to the neutral state, and a reverse drive
position corresponding to the reverse drive state;the control unit is
programmed to change, when the position of the first operation lever is
different from the position of the second operation lever, the steering
angle of at least one of the propulsion devices to facilitate the
behavior of the hull corresponding to the shift states of the respective
first and second propulsion device groups.

5. The marine vessel propulsion system according to claim 4, wherein the
control unit is programmed to control, when the first operation lever is
in the neutral position and the second operation lever is in a position
other than the neutral position, the shift state of the first propulsion
device group to be the neutral state and the shift state of the second
propulsion device group to be the forward or reverse drive state and to
change the steering angle of at least one of the propulsion devices so as
to face a direction to facilitate a turning motion of the hull
corresponding to a combination of the shift states of the respective
first and second propulsion device groups.

6. The marine vessel propulsion system according to claim 4, wherein the
control unit is programmed to change, when the first operation lever is
in one of the forward and reverse drive positions and the second
operation lever is in the other of the forward and reverse drive
positions, the steering angles of the respective first and second
propulsion device groups to bring a rear end portion of the first
propulsion device group and a rear end portion of the second propulsion
device group close to each other so that the hull pivots.

7. The marine vessel propulsion system according to claim 5, wherein the
control unit is programmed to maintain a certain amount of change in the
steering angle of each propulsion device regardless of an amount of
displacement of each operation lever with respect to the neutral
position.

8. The marine vessel propulsion system according to claim 5, wherein the
control unit is programmed to change an amount of change in the steering
angle of each propulsion device according to an amount of displacement of
each operation lever with respect to the neutral position.

9. The marine vessel propulsion system according to claim 1, further
comprising:a steering mechanism arranged to be operated by the marine
vessel maneuvering operator to change the steering angles of the
plurality of respective propulsion devices;a steering angle sensor
arranged to detect a rotation angle of the steering mechanism; anda
switching unit arranged to switch between normal marine vessel
maneuvering control and assisted marine vessel maneuvering control;
whereinin the normal marine vessel maneuvering control, the control unit
is programmed to control the shift states and propulsive forces of the
respective propulsion devices based on detection results from the
plurality of lever position sensors and to change the steering angles of
the respective propulsion devices based on a detection result from the
steering angle sensor; andin the assisted marine vessel maneuvering
control, the control unit is programmed to control, based on detection
results from the plurality of lever position sensors, the shift states
and propulsive forces of the respective propulsion devices and to change
the steering angle of at least one of the propulsion devices to
facilitate the behavior of the hull corresponding to the shift states of
the respective propulsion devices.

10. The marine vessel propulsion system according to claim 9, wherein in
the assisted marine vessel maneuvering control, the control unit is
programmed to control each of the propulsion devices to have a propulsive
force smaller than that corresponding to the position of each operation
lever in the normal marine vessel maneuvering control.

11. The marine vessel propulsion system according to claim 1, whereineach
of the propulsion devices includes an outboard motor arranged to be
mounted on the hull so as to enable the steering angle to change;the
outboard motor includes an engine with a driving force thereof being
adjustable through control of throttle opening degree, a propeller
arranged to be rotated by a driving force from the engine, and a
switching mechanism portion arranged to switch shift states;the operation
levers are arranged to be operated by the marine vessel maneuvering
operator to control the plurality of outboard motors of their respective
shift states and throttle opening degrees; andthe control unit is
programmed to control, based on detection results from the plurality of
lever position sensors, the shift states and throttle opening degrees of
the respective outboard motors and to change the steering angle of at
least one of the outboard motors to facilitate the behavior of the hull
corresponding to the shift states of the respective propulsion devices.

12. A marine vessel comprising:a hull;a plurality of propulsion devices
mounted on the hull so as to enable a steering angle to change;a
plurality of operation levers arranged to be operated by a marine vessel
maneuvering operator to control the plurality of propulsion devices to
change respective shift states selected from among a forward drive state,
a neutral state, and a reverse drive state;a plurality of lever position
sensors provided correspondingly to the plurality of respective operation
levers and arranged to detect positions of the operation levers; anda
control unit programmed to control, based on detection results from the
plurality of lever position sensors, the shift states of the respective
propulsion devices and to change the steering angle of at least one of
the propulsion devices to facilitate a behavior of the hull corresponding
to the shift states of the respective propulsion devices.

13. A marine vessel propulsion system comprising:a plurality of propulsion
devices arranged to be mounted on a hull so as to enable the steering
angle to change, the propulsion devices including a first propulsion
device group including at least one of the propulsion devices and a
second propulsion device group including at least one of the propulsion
devices not included in the first propulsion device group;a plurality of
operation levers arranged to be movable among a forward drive position
corresponding to a forward drive state, a neutral position corresponding
to a neutral state, and a reverse drive position corresponding to a
reverse drive state to control the plurality of propulsion devices to
change respective shift states selected from among the forward drive
state, neutral state, and reverse drive state, the operation levers
including a first operation lever corresponding to the first propulsion
device group and a second operation lever corresponding to the second
propulsion device group;a plurality of lever position sensors provided
correspondingly to the plurality of respective operation levers and
arranged to detect positions of the operation levers; anda control unit
programmed to control the shift states of the respective propulsion
devices based on detection results from the plurality of lever position
sensors and, when the first operation lever is in one of the forward and
reverse drive positions and the second operation lever is in the other of
the forward and reverse drive positions, to change the steering angles of
the respective first and second propulsion device groups to move a rear
end portion of the first propulsion device group and a rear end portion
of the second propulsion device group away from each other so that the
hull moves laterally.

14. The marine vessel propulsion system according to claim 13, wherein the
control unit is programmed to maintain a certain amount of change in the
steering angle of each propulsion device regardless of an amount of
displacement of each operation lever with respect to the neutral
position.

15. The marine vessel propulsion system according to claim 13, wherein the
control unit is programmed to change an amount of change in the steering
angle of each propulsion device according to an amount of displacement of
each operation lever with respect to the neutral position.

16. The marine vessel propulsion system according to claim 13, further
comprising:a steering mechanism arranged to be operated by a marine
vessel maneuvering operator to change the steering angles of the
plurality of respective propulsion devices;a steering angle sensor
arranged to detect a rotation angle of the steering mechanism; anda
switching unit arranged to switch between normal marine vessel
maneuvering control and assisted marine vessel maneuvering control;
whereinin the normal marine vessel maneuvering control, the control unit
is programmed to control the shift states and propulsive forces of the
respective propulsion devices based on detection results from the
plurality of lever position sensors and to change the steering angles of
the respective propulsion devices based on a detection result from the
steering angle sensor; andin the assisted marine vessel maneuvering
control, the control unit is programmed to control the shift states and
propulsive forces of the respective propulsion devices based on detection
results from the plurality of lever position sensors and, when the first
operation lever is in one of the forward and reverse drive positions and
the second operation lever is in the other of the forward and reverse
drive positions, to change the steering angles of the respective first
and second propulsion device groups to move the rear end portion of the
first propulsion device group and the rear end portion of the second
propulsion device group away from each other so that the hull moves
laterally.

17. The marine vessel propulsion system according to claim 16, wherein in
the assisted marine vessel maneuvering control, the control unit is
programmed to control each of the propulsion devices to have a propulsive
force smaller than that corresponding to the position of each operation
lever in the normal marine vessel maneuvering control.

18. The marine vessel propulsion system according to claim 13, whereineach
of the propulsion devices includes an outboard motor arranged to be
mounted on the hull so as to enable the steering angle to change;the
outboard motor includes an engine with a driving force thereof being
adjustable through control of throttle opening degree, a propeller
arranged to be rotated by a driving force from the engine, and a
switching mechanism portion arranged to switch shift states;the operation
levers are arranged to be operated by a marine vessel maneuvering
operator to control the plurality of outboard motors of their respective
shift states and throttle opening degrees; andthe control unit is
programmed to control the shift states and throttle opening degrees of
the respective outboard motors based on detection results from the
plurality of lever position sensors and, when the first operation lever
is in one of the forward and reverse drive positions and the second
operation lever is in the other of the forward and reverse drive
positions, to change the steering angles of the respective first and
second propulsion device groups to move an outboard motor rear end
portion of the first propulsion device group and an outboard motor rear
end portion of the second propulsion device group away from each other so
that the hull moves laterally.

19. A marine vessel comprising:a hull;a plurality of propulsion devices
mounted on the hull so as to enable a steering angle to change, the
propulsion devices including a first propulsion device group including at
least one of the propulsion devices and a second propulsion device group
including at least one of the propulsion devices not included in the
first propulsion device group;a plurality of operation levers arranged to
be movable among a forward drive position corresponding to a forward
drive state, a neutral position corresponding to a neutral state, and a
reverse drive position corresponding to a reverse drive state to control
the plurality of propulsion devices to change respective shift states
selected from among the forward drive state, neutral state, and reverse
drive state, the operation levers including a first operation lever
corresponding to the first propulsion device group and a second operation
lever corresponding to the second propulsion device group;a plurality of
lever position sensors provided correspondingly to the plurality of
respective operation levers and arranged to detect positions of the
operation levers; anda control unit programmed to control the shift
states of the respective propulsion devices based on detection results
from the plurality of lever position sensors and, when the first
operation lever is in one of the forward and reverse drive positions and
the second operation lever is in the other of the forward and reverse
drive positions, to change the steering angles of the respective first
and second propulsion device groups to move a rear end portion of the
first propulsion device group and a rear end portion of the second
propulsion device group away from each other so that the hull moves
laterally.

Description:

BACKGROUND OF THE INVENTION

[0001]1. Field of the Invention

[0002]The present invention relates to a marine vessel propulsion system
including operation levers arranged to be operated for controlling the
respective shift states of multiple propulsion devices. The present
invention also relates to a marine vessel including such a system.

[0003]2. Description of the Related Art

[0004]There has been known a marine vessel propulsion system including
operation levers arranged to be operated by a marine vessel maneuvering
operator to control the respective shift states of multiple propulsion
devices. One example of such a propulsion device is an outboard motor.

[0005]Such a marine vessel propulsion system includes, for example, two
outboard motors mounted on a hull. The two outboard motors are coupled to
each other with a tie bar and arranged to have substantially the same
steering angle. The marine vessel propulsion system further includes two
operation levers corresponding to the two respective outboard motors. The
shift state and throttle opening degree of each outboard motor can be
adjusted independently by operating the corresponding operation lever. In
addition, the two outboard motors are steerable through one steering
mechanism.

[0006]The thus arranged marine vessel propulsion system requires a
complicated operation when finely controlling the movement of the marine
vessel such as when launching from and docking on shore. That is, the
operator is required to finely control both the steering mechanism and
the two operation levers.

[0007]The hull may include a side thruster (propulsion device for lateral
movement) for easier marine vessel maneuvering when launching from and
docking on shore. This, however, results in the marine vessel propulsion
system having a complex structure, and is not suitable particularly for
small marine vessels.

[0008]United States Patent Application Publication No. US2007/0017426A1
discloses a marine vessel propulsion system that can finely control the
movement of the marine vessel easily without providing a side thruster.

[0009]This marine vessel propulsion system includes two operation levers
corresponding, respectively, to two outboard motors and a cross-shaped
key provided separately from the two operation levers. The shift state
and throttle opening degree of each outboard motor can be adjusted
independently by operating the corresponding operation lever. In
addition, the two outboard motors are steerable through one steering
mechanism. This marine vessel propulsion system can set a marine vessel
maneuvering support mode. In the marine vessel maneuvering support mode,
operating the cross-shaped key causes the steering angle, shift state,
and throttle opening degree of each outboard motor to be adjusted so that
the hull moves in the direction indicated by the cross-shaped key. This
allows the movement of the marine vessel to be controlled finely and
easily without a side thruster.

SUMMARY OF THE INVENTION

[0010]The inventors of preferred embodiments of the present invention
described and claimed in the present application conducted an extensive
study and research regarding a marine vessel propulsion system, such as
the one described above, and in doing so, discovered and first recognized
new unique challenges and previously unrecognized possibilities for
improvements as described in greater detail below.

[0011]That is, the related art above requires two operation levers and a
cross-shaped key to be provided separately, resulting in the marine
vessel propulsion system having a complex structure. That is, even though
no side thruster is provided, an additional operation system defined by
the cross-shaped key, must be provided in addition to the operation
levers and the steering mechanism. This results in complexity in the
structure and requires somewhat more complicated operations due to an
increase in the number of operation systems.

[0012]In order to overcome the previously unrecognized and unsolved
challenges described above, a preferred embodiment of the present
invention provides a marine vessel propulsion system including multiple
propulsion devices arranged to be mounted on a hull so as to enable a
steering angle to change, multiple operation levers, multiple lever
position sensors, and a control unit. The multiple operation levers are
arranged to be operated by a marine vessel maneuvering operator to
control changes in respective shift states of the multiple propulsion
devices selected from among a forward drive state, a neutral state, and a
reverse drive state. The multiple lever position sensors are provided
correspondingly to the multiple respective operation levers and arranged
to detect the positions of the operation levers. The control unit is
programmed to control the shift states of the respective propulsion
devices and to change the steering angle of at least one of the
propulsion devices based on detection results from the multiple lever
position sensors.

[0013]In the thus arranged marine vessel propulsion system, the shift
states of the respective propulsion devices are controlled and further
the steering angle of at least one of the propulsion devices is changed
based on detection results from the multiple lever position sensors. That
is, not only the shift states but also the steering angle follows the
detection results from the lever position sensors. This arrangement
allows the propulsive forces of the propulsion devices to act effectively
on the hull. This allows the hull to have a smaller turning radius, at
the time of turning movement of the hull, for example. It is further
possible to change the behavior of the hull quickly and highly
responsively. As a result, the movement of the marine vessel can be
precisely controlled.

[0014]In addition, since the marine vessel can be controlled only by
operating the operation levers, there is no need to operate the steering
mechanism. It is therefore possible to improve the operability when
finely controlling the movement of the marine vessel. There is also no
need to provide another operation system such as a cross-shaped key
separately from the operation levers, which can prevent the marine vessel
propulsion system from having a complex structure. Since there is no need
to add another operation system, no complicated operations are required.

[0015]In another preferred embodiment of the present invention, the
control unit is programmed to control, based on detection results from
the multiple lever position sensors, the shift states of the respective
propulsion devices and to change the steering angle of at least one of
the propulsion devices to facilitate the behavior of the hull
corresponding to the shift states of the respective propulsion devices.
This arrangement allows the propulsive forces of the propulsion devices
to act in the direction of the movement of the hull. This allows the hull
to have a smaller turning radius, at the time of turning movement of the
hull, for example. It is further possible to change the behavior of the
hull quickly and highly responsively. As a result, the movement of the
marine vessel can be precisely controlled.

[0016]The control unit is preferably programmed to control the shift
states of the respective propulsion devices based on detection results
from the multiple lever position sensors such that the positions of the
operation levers correspond to the shift states of the respective
propulsion devices.

[0017]With this arrangement, the positions of the operation levers
correspond to the shift states of the respective propulsion devices.
Thus, the operator can recognize in which direction a propulsive force is
applied to the hull while he or she operates the operation levers. This
allows the operator to easily imagine the behavior (e.g., turning motion,
pivoting motion) of the marine vessel caused by operating the operation
levers. In addition, controlling the steering angle allows the propulsive
forces of the propulsion devices to act in the direction of the movement
of the hull. It is therefore possible to achieve the behavior of the
marine vessel quickly and highly responsively as the operator imagines.
As a result, the operability of the marine vessel by the operator can be
further improved.

[0018]In the case described above, the multiple propulsion devices
preferably include a first propulsion device group including at least one
of the propulsion devices and a second propulsion device group including
at least one of the propulsion devices not included in the first
propulsion device group. Also, the multiple operation levers preferably
include a first operation lever corresponding to the first propulsion
device group and a second operation lever corresponding to the second
propulsion device group. Further, the control unit is preferably
programmed to change, when the position of the first operation lever is
different from the position of the second operation lever, the steering
angle of at least one of the propulsion devices to facilitate the
behavior of the hull corresponding to the shift states of the respective
first and second propulsion device groups. For example, the operator may
set the first and second operation levers in their respective different
positions to turn the hull. In this case, the hull can have a smaller
turning radius and it is possible to change the behavior of the hull
quickly and highly responsively.

[0019]Further, the first and second operation levers are preferably
arranged to be movable among a forward drive position corresponding to
the forward drive state, a neutral position corresponding to the neutral
state, and a reverse drive position corresponding to the reverse drive
state. Then, the control unit is preferably programmed to change, when
the position of the first operation lever (forward drive, neutral, or
reverse drive position) is different from the position of the second
operation lever (forward drive, neutral, or reverse drive position), the
steering angle of at least one of the propulsion devices to facilitate
the behavior of the hull corresponding to the shift states of the
respective first and second propulsion device groups.

[0020]In the case described above, the control unit is further preferably
programmed to control, when the first operation lever is in the neutral
position and the second operation lever is in a position other than the
neutral position, the shift state of the first propulsion device group to
be the neutral state and the shift state of the second propulsion device
group to be the forward or reverse drive state. Then, the control unit is
preferably programmed to change the steering angle of at least one of the
propulsion devices so as to face a direction for facilitating or
promoting the turning motion of the hull that occurs according to the
combination of the shift states of the respective first and second
propulsion device groups. With this arrangement, the hull can be applied
with a propulsive force in the turning direction to consequently have a
smaller turning radius. It is also possible to change the behavior of the
hull quickly and highly responsively.

[0021]The control unit is preferably programmed to change, when the first
operation lever is in one of the forward and reverse drive positions and
the second operation lever is in the other of the forward and reverse
drive positions, the steering angles of the respective first and second
propulsion device groups to bring the rear end portion of the first
propulsion device group and the rear end portion of the second propulsion
device group close to each other so that the hull pivots. This
arrangement allows the propulsive forces of the first and second
propulsion device groups to act in the pivoting direction of the hull.
That is, the hull can be applied with a propulsive force in a direction
deviated from the rotational center of the hull. This allows the hull to
rotate or pivot quickly and highly responsively without being largely
displaced, i.e., preferably with no displacement.

[0022]In a preferred embodiment of the present invention, the multiple
propulsion devices include a first propulsion device group including at
least one of the propulsion devices and a second propulsion device group
including at least one of the propulsion devices not included in the
first propulsion device group. Also, the multiple operation levers
include a first operation lever corresponding to the first propulsion
device group and a second operation lever corresponding to the second
propulsion device group. The first and second operation levers are
arranged to be movable among a forward drive position corresponding to
the forward drive state, a neutral position corresponding to the neutral
state, and a reverse drive position corresponding to the reverse drive
state. Further, the control unit is programmed to change, when the first
operation lever is in one of the forward and reverse drive positions and
the second operation lever is in the other of the forward and reverse
drive positions, the steering angles of the respective first and second
propulsion device groups to move the rear end portion of the first
propulsion device group and the rear end portion of the second propulsion
device group away from each other so that the hull moves laterally. More
specifically, the propulsive forces of the first and second propulsion
device groups act on the hull toward the rotational center thereof.
Therefore, the hull cannot be applied with a large moment, and the hull
moves laterally, for example, in the direction of the resultant vector of
propulsive force vectors generated by the first and second propulsion
device groups. Thus, the hull can move laterally with the propulsive
forces of the first and second propulsion device groups without providing
a side thruster on the hull.

[0023]In a preferred embodiment of the present invention, the control unit
is programmed to maintain a certain amount of change in the steering
angle of each propulsion device regardless of the amount of displacement
of each operation lever with respect to the neutral position. This
arrangement allows the change in the behavior (speed) of the hull to be
adjusted in faithful accordance with the operation amount of each
operation lever.

[0024]In another preferred embodiment of the present invention, the
control unit is programmed to change the amount of change in the steering
angle of each propulsion device according to the amount of displacement
of each operation lever with respect to the neutral position. With this
arrangement, the amount of change in the steering angle of each
propulsion device can be increased by increasing the amount of operation
of each operation lever. This allows a turning or pivoting force to act
more forcefully on the hull, for example, when the amount of operation of
each operation lever is increased. This allows the hull to have a smaller
turning radius and it is possible to change the behavior of the hull more
quickly and highly responsively.

[0025]The marine vessel propulsion system according to a preferred
embodiment of the present invention further includes a steering mechanism
arranged to be operated by a marine vessel maneuvering operator to change
the steering angles of the respective propulsion devices, a steering
angle sensor arranged to detect the rotation angle of the steering
mechanism, and a switching unit arranged to switch between normal marine
vessel maneuvering control and assisted marine vessel maneuvering
control. In this case, it is preferred that in the normal marine vessel
maneuvering control, the control unit is programmed to control the shift
states and propulsive forces of the respective propulsion devices based
on detection results from the multiple lever position sensors and to
change the steering angles of the respective propulsion devices based on
a detection result from the steering angle sensor. It is also preferred
that in the assisted marine vessel maneuvering control, the control unit
is programmed to control the shift states and propulsive forces of the
respective propulsion devices based on detection results from the
multiple lever position sensors and to change the steering angle of at
least one of the propulsion devices. In the normal control, the operator
can use the steering mechanism for steering. When it is required to
finely control the movement of the marine vessel (such as when launching
from and docking on shore), the operator can use only the operation
levers for steering by switching to the assisted marine vessel
maneuvering control. This can improve the convenience for operators.

[0026]In the case described above, the control unit may be programmed to
control, in the assisted marine vessel maneuvering control, each
propulsion device to have a propulsive force smaller than that
corresponding to the position of each operation lever in the normal
marine vessel maneuvering control.

[0027]Preferably, the propulsion devices each include an outboard motor
arranged to be mounted on the hull so as to enable a steering angle to
change. The outboard motor includes, for example, an engine with the
driving force thereof being adjustable through control of throttle
opening degree, a propeller arranged to be rotated by a driving force
from the engine, and a switching mechanism portion arranged to switch
shift states. The operation levers are preferably arranged to be operated
by a marine vessel maneuvering operator to control respective shift
states of the multiple outboard motors and throttle opening degrees of
the outboard motors. The control unit is preferably programmed to control
the shift states and throttle opening degrees of the respective outboard
motors based on detection results from the multiple lever position
sensors and to change the steering angle of at least one of the outboard
motors. With this arrangement, the marine vessel propulsion system
including outboard motors can improve the operability when finely
controlling the movement of the marine vessel.

[0028]A preferred embodiment of the present invention provides a marine
vessel including a hull and a marine vessel propulsion system mounted on
the hull and having the above-described features. This arrangement can
improve the operability when finely controlling the movement of the
marine vessel while preventing the marine vessel propulsion system from
having a complex structure.

[0029]Other elements, features, steps, characteristics and advantages of
the present invention will become more apparent from the following
detailed description of the preferred embodiments with reference to the
attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a perspective view of a marine vessel including a marine
vessel propulsion system according to a first preferred embodiment of the
present invention.

[0032]FIG. 3 is a schematic plan view of a control lever in the marine
vessel propulsion system.

[0033]FIG. 4 is a side view of an outboard motor in the marine vessel
propulsion system.

[0034]FIG. 5 is a block diagram showing the electrical configuration of
the marine vessel propulsion system.

[0035]FIG. 6 illustrates steering angle control when the marine vessel
propulsion system is in an assisted marine vessel maneuvering mode.

[0036]FIG. 7 shows the relationship between the position of each operation
lever and the shift state as well as steering angle of each outboard
motor when the marine vessel propulsion system is in the assisted marine
vessel maneuvering mode.

[0037]FIG. 8 is a flow chart illustrating the control of the marine vessel
propulsion system.

[0039]FIG. 13 illustrates steering angle control when a marine vessel
propulsion system according to a second preferred embodiment of the
present invention is in an assisted marine vessel maneuvering mode.

[0040]FIG. 14 shows the relationship between the position of each
operation lever and the shift state as well as steering angle of each
outboard motor when the marine vessel propulsion system according to the
second preferred embodiment is in the assisted marine vessel maneuvering
mode.

[0041]FIG. 15 shows the relationship between the amount of displacement of
each operation lever and the steering angle when the marine vessel
propulsion system according to the second preferred embodiment is in the
assisted marine vessel maneuvering mode.

[0042]FIG. 16 illustrates steering angle control when a marine vessel
propulsion system according to a third preferred embodiment of the
present invention is in an assisted marine vessel maneuvering mode.

[0043]FIG. 17 shows the relationship between the position of each
operation lever and the shift state as well as steering angle of each
outboard motor when the marine vessel propulsion system according to the
third preferred embodiment is in the assisted marine vessel maneuvering
mode.

[0044]FIG. 18 illustrates the change in the lateral movement speed when
the marine vessel propulsion system according to the third preferred
embodiment is in the assisted marine vessel maneuvering mode.

[0045]FIG. 19 shows the change in the lateral movement speed when the
marine vessel propulsion system according to the third preferred
embodiment is in the assisted marine vessel maneuvering mode.

[0046]FIG. 20 shows the relationship between the position of each
operation lever and the shift state as well as steering angle of each
outboard motor when a marine vessel propulsion system according to a
fourth preferred embodiment of the present invention is in an assisted
marine vessel maneuvering mode.

[0047]FIG. 21 illustrates steering angle control when a marine vessel
propulsion system according to a fifth preferred embodiment of the
present invention is in an assisted marine vessel maneuvering mode.

[0048]FIG. 21A is a block diagram showing the electrical configuration of
the marine vessel propulsion system.

[0049]FIG. 22 illustrates steering angle control when a marine vessel
propulsion system according to a sixth preferred embodiment of the
present invention is in an assisted marine vessel maneuvering mode.

[0050]FIG. 22A is a block diagram showing the electrical configuration of
the marine vessel propulsion system.

[0051]FIG. 23 shows throttle opening degree control when a marine vessel
propulsion system according to an exemplary variation of the first
preferred embodiment of the present invention is in normal and assisted
marine vessel maneuvering modes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

[0052]The structure of a marine vessel propulsion system according to a
first preferred embodiment of the present invention will be described
with reference to FIGS. 1 to 5.

[0053]Two outboard motors 300 (right outboard motor 301 and left outboard
motor 302) are mounted at the stern 101 of a hull 100 via two steering
units 200 (right steering unit 201 and left steering unit 202) (see FIGS.
2 and 5). A remote control lever 102, a steering mechanism 103, a hull
ECU (Electronic Control Unit) 104, a trim switch (not shown), and the
like are arranged on the hull 100. The remote control lever 102 is
arranged to be operated by a marine vessel maneuvering operator to
control switching the throttle opening degrees and shift states of the
outboard motors 300. The steering mechanism 103 is arranged to be
operated by the operator to change the heading direction of the hull 100.
The hull ECU 104 is programmed to control the marine vessel propulsion
system. The trim switch is arranged to be operated by the operator to
change the mounting angle of the outboard motors 300 with respect to the
hull 100. The outboard motors 300 and the hull ECU 104 are, respectively,
examples of "propulsion devices" and "control unit" according to a
preferred embodiment of the present invention.

[0054]The remote control lever 102 includes two operation levers (right
operation lever 102a and left operation lever 102b) that correspond to
the respective right and left outboard motors 301 and 302. The right and
left operation levers 102a and 102b are arranged laterally (in the
direction A) and are arranged to be movable longitudinally (in the
direction B) independently of each other. The operator can switch the
shift state and perform acceleration control (throttle opening degree
control) of the right outboard motor 301 by operating the right operation
lever 102a. The operator can also switch the shift state and perform
acceleration control of the left outboard motor 302 by operating the left
operation lever 102b. The shift state of the outboard motors 301 and 302
can be selected from among neutral state, forward drive state, and
reverse drive state. The right and left operation levers 102a and 102b
are, respectively, examples of "first operation lever" and "second
operation lever" according to a preferred embodiment of the present
invention. Also, the right and left outboard motors 301 and 302 are,
respectively, examples of "first propulsion device group" and "second
propulsion device group" according to a preferred embodiment of the
present invention.

[0055]As shown in FIG. 3, the operation levers (right operation lever 102a
and left operation lever 102b) are movable among a neutral position, a
forward drive position, and a reverse drive position. The neutral
position, forward drive position, and reverse drive position correspond,
respectively, to the neutral state, forward drive state, and reverse
drive state of the outboard motors 300. The marine vessel propulsion
system is arranged to change the throttle opening degree of each outboard
motor 300 according to the amount of displacement of the corresponding
operation lever with respect to the neutral position when the operation
lever is in the forward or reverse drive position. That is, the greater
the amount of displacement of the operation lever with respect to the
neutral position, the greater the throttle opening degree of the
corresponding outboard motor 300 becomes. The remote control lever 102
includes lever position sensors 102c and 102d arranged to detect the
turning angle of the operation levers, being provided correspondingly to
the respective right and left operation levers 102a and 102b. The shift
states and throttle opening degrees of the respective outboard motors 300
(right outboard motor 301 and left outboard motor 302) are controlled
based on detection results from the lever position sensors 102c and 102d.

[0056]The steering mechanism 103 is also arranged to be operated by the
operator to steer the outboard motors 300 (right outboard motor 301 and
left outboard motor 302). The steering mechanism 103 is provided with a
steering angle sensor 103a arranged to detect the turning angle of the
steering mechanism 103.

[0057]The steering units 200 (right steering unit 201 and left steering
unit 202) are each mounted at the stern 101 of the hull 100 via a clamp
bracket 400. As shown in FIG. 5, the right steering unit 201 includes a
motor 201a arranged to turn the corresponding outboard motor 300 during
steering, an actual rudder angle sensor 201b arranged to detect the
turning angle (actual rudder angle) of the outboard motor 300, and a
steering ECU 201c. Similarly, the left steering unit 202 includes a motor
202a arranged to turn the corresponding outboard motor 300 during
steering, an actual rudder angle sensor 202b arranged to detect the
turning angle (actual rudder angle) of the outboard motor 300, and a
steering ECU 202c. The hull ECU 104 and the steering ECUs 201c and 202c
are arranged to be capable of communicating information with each other
via a LAN (local area network) 10 built in the hull 100.

[0058]When the motors 201a and 202a are driven based on a detection result
from the steering angle sensor 103a, the steering angles of the outboard
motors 300 (right outboard motor 301 and left outboard motor 302) are
adjusted accordingly. That is, when the bodies of the outboard motors 300
are turned horizontally, propellers 307 change their direction. This
changes the heading direction of the hull 100 that depends on propulsive
forces generated by the propellers 307.

[0059]The steering units 200 can change the steering angle of each
outboard motor 300 preferably within an angular range of about 60 degrees
(±30 degrees), for example. When the steering angles of the outboard
motors 300 are adjusted based on a detection result from the steering
angle sensor 103a, the motors 201a and 202a are controlled such that the
right and left outboard motors 301 and 302 have substantially the same
steering angle.

[0060]As shown in FIG. 4, the outboard motors 300 each include an engine
303, a drive shaft 304, a forward-reverse switching mechanism 305, a
propeller shaft 306, a propeller 307, and an outboard motor ECU 308. The
engine 303 is arranged to generate a driving force by burning a mixture
of air and fuel. The drive shaft 304 extends in the vertical direction
(in the Z direction) and is arranged to be rotated by a driving force
from the engine 303. The forward-reverse switching mechanism 305 is
connected to the lower end of the drive shaft 304. The propeller shaft
306 is connected to the forward-reverse switching mechanism 305 and
extends in the horizontal direction. The propeller 307 is fixed at the
rear end portion of the propeller shaft 306. The outboard motor ECU 308
is arranged to control the operations of the engine 303 and the
forward-reverse switching mechanism 305. The hull ECU 104 and the
outboard motor ECUs 308 in the right and left outboard motors are
arranged to be capable of communicating information with each other via
the LAN 10.

[0061]The engine 303 includes a motor 303a and a throttle valve 303b. The
throttle valve 303b is provided in a feed path for feeding air
therethrough into a mixture combustion chamber (not shown). The throttle
valve 303b is arranged to be opened and closed by a driving force from
the motor 303a within the range from the fully-closed state (with an
opening degree of 0%) to the fully-opened state (with an opening degree
of 100%). The motor 303a is controlled by the outboard motor ECU 308. The
driving force of the engine 303 can be adjusted by controlling the
opening degree (throttle opening degree) of the throttle valve 303b and
therefore the feed amount of air.

[0062]The forward-reverse switching mechanism 305 is arranged to set a
shift state selected from among forward drive state, reverse drive state,
and neutral state. The forward drive state is a shift state in which the
rotation of the drive shaft 304 caused by a driving force from the engine
303 is transmitted to rotate the propeller shaft 306 in the forward drive
direction. The reverse drive state is a shift state in which the rotation
of the drive shaft 304 is reversed and transmitted to rotate the
propeller shaft 306 in the reverse drive direction. The neutral state is
a shift state in which the transmitting of the rotation from the drive
shaft 304 to the propeller shaft 306 is blocked off. The shift state is
switched by a driving force from a motor 305a. The motor 305a is
controlled by the outboard motor ECU 308.

[0063]The outboard motor ECU 308 controls the motors 303a and 305a and
other electrical components in the outboard motor 300 based on signals
from the hull ECU 104. The forward-reverse switching mechanism 305 is an
example of a "switching mechanism portion" according to a preferred
embodiment of the present invention.

[0064]The engine 303 is housed in an engine cover 309. An upper case 310
and a lower case 311 are arranged below the engine cover 309, and the
drive shaft 304 and the forward-reverse switching mechanism 305 as well
as the propeller shaft 306 are housed in the respective cases 310 and
311. A ventilation hole 309a is provided in a lateral portion of the
engine cover 309 on the side of reverse drive direction (indicated by the
arrow B1). Air which is introduced in the engine cover 309 via the
ventilation hole 309a, is fed to the engine 303.

[0065]The outboard motors 300 are each mounted at the stern 101 of the
hull 100 via a clamp bracket 400. The clamp bracket 400 supports each
outboard motor 300 in a vertically swingable manner about a tilting shaft
400a with respect to the hull 100.

[0066]The hull 100 is provided with a selector switch 105 to be operated
by the operator to switch control modes. The control modes include a
normal marine vessel maneuvering mode in which the steering mechanism 103
is used for marine vessel maneuvering and an assisted marine vessel
maneuvering mode in which the steering mechanism 103 is not required to
be used for marine vessel maneuvering. One of these control modes can be
selected by operating the selector switch 105.

[0067]In the normal marine vessel maneuvering mode, the shift states and
throttle opening degrees of the respective right and left outboard motors
301 and 302 are controlled based on detection results from the lever
position sensors 102c and 102d. The steering angle of the outboard motors
300 (right outboard motor 301 and left outboard motor 302) is also
controlled based on a detection result from the steering angle sensor
103a.

[0068]In the assisted marine vessel maneuvering mode, the shift states,
throttle opening degrees, and steering angles of the respective right and
left outboard motors 301 and 302 are controlled based on detection
results from the lever position sensors 102c and 102d.

[0069]The operator can switch between the normal marine vessel maneuvering
mode and the assisted marine vessel maneuvering mode by switching the
selector switch 105 ON and OFF. That is, when the selector switch 105 is
OFF, the normal marine vessel maneuvering mode runs. When the selector
switch 105 is ON, the assisted marine vessel maneuvering mode runs. In
the assisted marine vessel maneuvering mode, when the steering mechanism
103 is operated, the selector switch 105 is turned OFF automatically by
the control of the hull ECU 104 and the normal marine vessel maneuvering
mode runs automatically. The selector switch 105 is an example of a
"switching unit" according to a preferred embodiment of the present
invention.

[0070]Next will be described the control when the marine vessel propulsion
system according to the first preferred embodiment of the present
invention is in the assisted marine vessel maneuvering mode with
reference to FIGS. 6 and 7. It is noted that the "propulsive direction"
indicated by the arrows in FIG. 6 is a direction of a propulsive force
applied to the hull 100 by the right and left outboard motors 301 and
302. The length of each arrow represents the magnitude of a propulsive
force by the right and left outboard motors 301 and 302.

[0071]As shown in FIG. 7, in the assisted marine vessel maneuvering mode,
the positions of the operation levers (forward drive, reverse drive, and
neutral positions) correspond to the shift states of the respective
outboard motors 300 (forward drive (F), reverse drive (R), and neutral
(N)). The amount of displacement of each operation lever with respect to
the neutral position also corresponds to the throttle opening degree,
though not shown in the figure. Therefore, the relationship between the
position of each operation lever and the shift state as well as throttle
opening degree of each outboard motor 300 is substantially the same as in
the normal marine vessel maneuvering mode.

[0072]When the shift state of the right outboard motor 301 corresponding
to the position of the right operation lever 102a is the same as the
shift state of the left outboard motor 302 corresponding to the position
of the left operation lever 102b, the operation is the same as in the
normal marine vessel maneuvering mode. That is, the steering angle of the
outboard motors 300 is not changed, and only the shift states and
throttle opening degrees of the outboard motors 300 are changed.
Specifically, when both the right and left operation levers 102a and 102b
are in the neutral position, the shift states of the right and left
outboard motors 301 and 302 are both neutral (N). In this case, the
throttle opening degrees of the right and left outboard motors 301 and
302 are both in the fully-closed state (with an opening degree of 0%).
When both the right and left operation levers 102a and 102b are in the
forward or reverse drive position, the shift states of the right and left
outboard motors 301 and 302 are both forward drive (F) or reverse drive
(R). Then, the right and left outboard motors 301 and 302 have their
respective throttle opening degrees (0 to 100%) that correspond to the
amount of displacement of the respective operation levers with respect to
the neutral position.

[0073]When the shift states of the right and left outboard motors 301 and
302 are different from each other, not only the shift states and throttle
opening degrees of the outboard motors 300 but also the steering angles
of the outboard motors 300 are changed. That is, the steering angles of
the outboard motors 300 are changed to promote the behavior of the hull
100 according to a propulsive force generated by the outboard motors 300.

[0074]For example, as indicated by (A1) in FIG. 7, when the right and left
operation levers 102a and 102b are, respectively, in the neutral and
forward drive positions, the shift states of the right and left outboard
motors 301 and 302 are, respectively, neutral (N) and forward drive (F).
In this case, since a forward drive propulsive force is applied only on
the left side of the hull 100 as shown in (A1) of FIG. 6, the behavior of
the hull 100 is a right-forward turning motion. In this case, the
steering angle of the left outboard motor 302 that generates a propulsive
force is changed to be about +10 degrees, for example, so as to follow
the right-forward turning direction of the hull 100. The steering angle
of the right outboard motor 301 is kept at 0 degrees. Similarly, as
indicated by (A2) in FIG. 7, when the right and left operation levers
102a and 102b are, respectively, in the forward drive and neutral
positions, the steering angle of the right outboard motor 301 that
generates a propulsive force is changed to be about -10 degrees, for
example, so as to follow the left-forward turning direction of the hull
100. The steering angle of the left outboard motor 302 is kept at 0
degrees. It is noted that the steering angle takes a positive value when
the rear end portions (propellers 307) of the outboard motors 301 and 302
are turned rightward with respect to the longitudinal direction of the
hull 100, while taking a negative value when turned leftward.

[0075]As indicated by (B1) in FIG. 7, when the right and left operation
levers 102a and 102b are, respectively, in the neutral and reverse drive
positions, the shift states of the right and left outboard motors 301 and
302 are, respectively, neutral (N) and reverse drive (R). In this case,
since a reverse drive propulsive force is applied only on the left side
of the hull 100 as shown in (B1) of FIG. 6, the behavior of the hull 100
is a right-backward turning motion. In this case, the steering angle of
the left outboard motor 302 that generates a propulsive force is changed
to be about +10 degrees, for example, so as to follow the right-backward
turning direction of the hull 100. The steering angle of the right
outboard motor 301 is kept at 0 degrees. Similarly, as indicated by (B2)
in FIG. 7, when the right and left operation levers 102a and 102b are,
respectively, in the reverse drive and neutral positions, the steering
angle of the right outboard motor 301 that generates a propulsive force
is changed to be about -10 degrees, for example, so as to follow the
left-backward turning direction of the hull 100. The steering angle of
the left outboard motor 302 is kept at 0 degrees.

[0076]Also, as indicated by (C1) in FIG. 7, when the right and left
operation levers 102a and 102b are, respectively, in the reverse and
forward drive positions, the shift states of the right and left outboard
motors 301 and 302 are, respectively, reverse drive (R) and forward drive
(F). In this case, since a forward drive propulsive force is applied on
the left side of the hull 100 and a reverse drive propulsive force is
applied on the right side of the hull 100 as shown in (C1) of FIG. 6, the
behavior of the hull 100 is a rightward pivoting motion about the stern
of the hull 100. In this case, the steering angle of the left outboard
motor 302 is changed to be about +10 degrees, for example, so as to
follow the rightward pivoting direction of the hull 100 and the steering
angle of the right outboard motor 301 is changed to be about -10 degrees,
for example, so as to follow the rightward pivoting direction of the hull
100. Similarly, as indicated by (C2) in FIG. 7, when the right and left
operation levers 102a and 102b are, respectively, in the forward and
reverse drive positions, the steering angle of the left outboard motor
302 is changed to be about +10 degrees, for example, so as to follow the
leftward pivoting direction of the hull 100 and the steering angle of the
right outboard motor 301 is changed to be about -10 degrees, for example,
so as to follow the leftward pivoting direction of the hull 100. That is,
when the right and left operation levers 102a and 102b are, respectively,
in one and the other of the forward and reverse drive positions, the
steering angles of the right and left outboard motors 301 and 302 are
changed such that the rear end portions of the right and left outboard
motors 301 and 302 are brought close to each other.

[0077]The vector directions of the propulsive forces generated by the
right and left outboard motors 300 do not include the rotational center
of the hull 100 (that approximately coincides with the center of gravity
of the hull 100, for example). Therefore, the propulsive forces generated
by the right and left outboard motors 300 apply a moment about a vertical
axis to the hull 100. This causes the hull 100 to pivot with little
displacement.

[0078]Further, as shown in (D) of FIG. 6, the hull 100 can move laterally
by combining the operations of the patterns (A1), (A2), (B1), (B2), (C1),
and (C2). For example, the hull 100 can move leftward by repeating the
operations (A1) and (B1) alternately. In this case, the operation (A1)
causes the stern of the hull 100 to move leftward and the operation (B1)
causes the stem of the hull 100 to move leftward. Since the resistance
from water that the hull 100 undergoes is different between forward drive
and reverse drive, performing the operation (A1) and then (B1) causes the
stem of the hull 100 to pivot leftward with little displacement of the
stern. This allows the hull 100 to move leftward laterally. Also, the
hull 100 can move rightward laterally by repeating the operations of the
patterns (A2) and (B2) alternately as shown in FIG. 7. The hull 100 can
move laterally in any direction by combining these leftward and rightward
drives and the pivoting operation (C1) and/or (C2).

[0079]In the first preferred embodiment, the amount of change in the
steering angle of a turned outboard motor 300 is preferably fixed at
about 10 degrees, for example, regardless of the amount of displacement
of the corresponding operation lever with respect to the neutral position
(i.e., throttle opening degree). In the marine vessel propulsion system
adopting two outboard motors 300, when the steering angles of the right
and left outboard motors 301 and 302 are changed by, for example, about
13 degrees or more so that the rear end portions thereof are brought
close to each other, the right and left outboard motors 301 and 302
interfere with each other. Accordingly, the amount of change in the
steering angle of each outboard motor 300 is preferably set to about 12
degrees or less, for example.

[0080]Next will be described the operational control for the marine vessel
propulsion system according to the first preferred embodiment of the
present invention with reference to FIGS. 7 and 8.

[0081]In Step S1, the hull ECU 104 determines whether or not the selector
switch 105 is ON. If the selector switch 105 is OFF, the routine goes to
Step S7 and the control under the normal marine vessel maneuvering mode
is performed. On the other hand, if the selector switch 105 is ON, the
control under the assisted marine vessel maneuvering mode is performed in
Step S2.

[0082]In the normal marine vessel maneuvering mode, the hull ECU 104
determines the shift states and throttle opening degrees of the right and
left outboard motors 301 and 302 based on positional information of the
operation levers detected by the lever position sensors 102c and 102d.
These determined shift states and throttle opening degrees are sent to
the outboard motor ECUs 308. The outboard motor ECUs 308 control the
motors 303a and 305a based on the received shift information and throttle
opening degrees to drive the throttle valve 303b and the forward-reverse
switching mechanism 305. The hull ECU 104 also determines the steering
angles of the right and left outboard motors 301 and 302 based on a
steering angle detected by the steering angle sensor 103a, and sends the
determined steering angle data to the steering ECUs 201c and 202c. The
steering ECUs 201c and 202c drive the motors 201a and 202a in the
respective right and left steering units 201 and 202 to make actual
rudder angles detected by the respective actual rudder angle sensors 201b
and 202b to equal to the received steering angles.

[0083]On the other hand, in the assisted marine vessel maneuvering mode,
the lever position sensors 102c and 102d detect the positions of the
respective operation levers (right operation lever 102a and left
operation lever 102b) in Step S3. The positional information of the
operation levers is sent from the lever position sensors 102c and 102d to
the hull ECU 104. Then, in Step S4, the hull ECU 104 determines the shift
states, throttle opening degrees, and steering angles of the right and
left outboard motors 301 and 302 based on the received positional
information of the operation levers and the relationship shown in FIG. 7.

[0084]Next, in Step S5, the hull ECU 104 sends the determined shift states
and throttle opening degrees to the outboard motor ECUs 308 in the right
and left outboard motors 301 and 302. The outboard motor ECUs 308 drive
the motor 305a for the forward-reverse switching mechanism 305 and the
motor 303a for the throttle valve 303b to achieve the received shift
states and throttle opening degrees. The hull ECU 104 also sends the
determined steering angles to the steering ECUs 201c and 202c in the
respective right and left steering units 201 and 202. The steering ECUs
201c and 202c drive the motors 201a and 202a in the respective right and
left steering units 201 and 202 to make actual rudder angles detected by
the respective actual rudder angle sensors 201b and 202b to equal to the
received steering angles.

[0085]In Step S6, the hull ECU 104 determines whether or not the steering
mechanism 103 is operated based on a detection result from the steering
angle sensor 103a. If the steering mechanism 103 is rotated by a
predetermined angle or more, the hull ECU 104 determines that the
steering mechanism 103 is operated by the operator, and the routine
proceeds to Step S7 to switch to the control under the normal marine
vessel maneuvering mode. If the steering mechanism 103 is not rotated by
the predetermined angle or more, the hull ECU 104 determines that the
steering mechanism 103 is not operated by the operator, and the routine
returns to Step S1. Steps S1 to S7 will thereafter be repeated.

[0086]In the assisted marine vessel maneuvering mode, not only the shift
states and propulsive forces but also the steering angles of the right
and left outboard motors 301 and 302 are controlled based on detection
results from the two lever position sensors 102c and 102d, as described
above. More specifically, the steering angles of the right and left
outboard motors 301 and 302 are changed to facilitate the behavior of the
hull 100 corresponding to the shift states and propulsive forces of the
right and left outboard motors 301 and 302. This allows the propulsive
forces of the outboard motors 300 to act effectively on the hull 100.
This allows the hull 100 to have a smaller turning radius. It is further
possible to change the behavior of the hull 100 quickly. As a result, the
movement of the marine vessel can be controlled finely. In addition,
since the marine vessel can be controlled only by operating the operation
levers (right operation lever 102a and left operation lever 102b), there
is no need to operate the steering mechanism 103. It is therefore
possible to improve the operability when finely controlling the movement
of the marine vessel. Since the marine vessel can be controlled only by
operating the operation levers, there is also no need to provide another
operation system such as a cross-shaped key separately from the operation
levers, which can prevent the marine vessel propulsion system from having
a complex structure as well as the operations being complicated.

[0087]Also, in the assisted marine vessel maneuvering mode, the shift
states and propulsive forces of the outboard motors 300 are controlled
such that the positions of the operation levers correspond to the shift
states and the throttle opening degrees. Therefore, the positions of the
respective right and left operation levers 102a and 102b correspond to
the shift states of the respective right and left outboard motors 301 and
302. Thus, the operator can recognize in which direction a propulsive
force is applied to the hull 100 while he or she operates the operation
levers. This allows the operator to easily imagine the behavior of the
marine vessel, such as turning motion and pivoting motion, caused by
operating the operation levers. In addition, controlling the steering
angle allows the propulsive forces of the outboard motors 300 to act in
the direction of the movement of the hull 100. It is therefore possible
to achieve the behavior of the marine vessel quickly and highly
responsively as the operator imagines. As a result, the operability of
the marine vessel by the operator can be further improved.

[0088]Further, in the assisted marine vessel maneuvering mode, when the
positions of the respective right and left operation levers 102a and 102b
are different from each other, the steering angles of the outboard motors
300 are changed to promote the behavior of the hull 100 corresponding to
the shift states and propulsive forces of the right and left outboard
motors 301 and 302. With this arrangement, when the operator operates the
right and left operation levers 102a and 102b to be their respective
different positions to turn the hull 100, the hull 100 can be turned with
a small turning radius, and it is also possible to change the behavior of
the hull 100 quickly and highly responsively.

[0089]Furthermore, in the assisted marine vessel maneuvering mode, when
the right and left operation levers 102a and 102b are, respectively, in
the forward and reverse drive positions, the steering angles of the right
and left outboard motors 301 and 302 are changed such that the rear end
portions of the respective outboard motors 301 and 302 are brought close
to each other. This causes the hull 100 to pivot. This arrangement allows
the propulsive forces of the right and left outboard motors 301 and 302
to act in the pivoting direction of the hull. That is, the hull 100 can
be applied with a propulsive force in a direction deviated from the
rotational center of the hull 100. This allows the hull 100 to rotate
(pivot) quickly without being largely displaced (substantially with no
displacement).

[0090]Also, in the assisted marine vessel maneuvering mode, as described
above, a certain amount of change in the steering angle of each outboard
motor 300 is maintained regardless of the amount of displacement of each
operation lever with respect to the neutral position. This allows the
change in the behavior (speed) of the hull 100 to be adjusted in faithful
accordance with the amount of control of each operation lever.

[0091]Moreover, in the first preferred embodiment, the selector switch 105
is arranged to switch control modes between the normal marine vessel
maneuvering mode and the assisted marine vessel maneuvering mode, as
described above. With this arrangement, the operator can run the normal
marine vessel maneuvering mode and use the steering mechanism 103 for
normal marine vessel maneuvering. On the other hand, the operator, when
required to finely control the movement of the marine vessel (such as
launching from and docking on shore), can run the assisted marine vessel
maneuvering mode and use only the operation levers for maneuvering. This
can improve the convenience for the operator.

[0092]The above-described advantageous effects of the marine vessel
propulsion system according to the first preferred embodiment of the
present invention will hereinafter be described in more detail with
reference to FIGS. 9 to 12. In the following descriptions, the behavior
of the marine vessel propulsion system in the normal marine vessel
maneuvering mode, in which the steering angles of the outboard motors 300
are not controlled using the operation levers, are shown in a manner
comparable with those in the assisted marine vessel maneuvering mode.

[0093]FIG. 9 shows the behavior of the hull 100 when turned only by
operating the operation levers under the assisted and normal marine
vessel maneuvering modes according to the first preferred embodiment. As
shown in FIG. 9, in the normal marine vessel maneuvering mode, since the
turning direction is different from the direction in which the propulsive
forces of the outboard motors 300 are applied, the turning speed is low.
This results in a larger turning radius in the normal marine vessel
maneuvering mode. On the other hand, in the assisted marine vessel
maneuvering mode, since the propulsive forces of the outboard motors 300
are applied in the turning direction, the turning speed is high to result
in a smaller turning radius.

[0094]FIG. 10 shows the behavior of the hull 100 when put between piers
only by operating the operation levers under the assisted and normal
marine vessel maneuvering modes. As shown in FIG. 10, in the normal
marine vessel maneuvering mode, the hull 100 cannot be turned in a small
radius due to its low turning speed and pivoting speed, which requires a
larger space R1 to put the marine vessel between the piers. On the other
hand, in the assisted marine vessel maneuvering mode, the turning speed
and pivoting speed are both high, which requires only a smaller space S1
to put the marine vessel between the piers.

[0095]FIG. 11 shows the behavior of the hull 100 when brought alongside a
pier under the assisted and normal marine vessel maneuvering modes. As
shown in FIG. 11, in the normal marine vessel maneuvering mode, the hull
100 cannot be turned in a small radius due to its low turning speed and
pivoting speed, which requires a larger space R2 to bring the marine
vessel alongside the pier. On the other hand, in the assisted marine
vessel maneuvering mode, the turning speed and pivoting speed are both
high, which requires only a smaller space S2 to bring the marine vessel
alongside the pier.

[0096]FIG. 12 shows the behavior of the hull 100 when pivoting only by
operating the operation levers under the assisted and normal marine
vessel maneuvering modes with the wind from a certain direction. The hull
100 is required to move faster under the wind. As shown in FIG. 12, in
the normal marine vessel maneuvering mode, since the pivoting direction
is different from the direction in which the propulsive forces of the
outboard motors 300 are applied, the pivoting speed is low. For this
reason, the hull 100 is displaced largely by the wind during pivoting. On
the other hand, in the assisted marine vessel maneuvering mode, since the
propulsive forces of the outboard motors 300 are applied in the pivoting
direction, the pivoting speed is high. For this reason, the hull 100 is
less likely to be displaced during pivoting.

Second Preferred Embodiment

[0097]Referring now to FIGS. 13 to 15, in the second preferred embodiment,
the amount of change in the steering angle of each outboard motor 300 is
changed according to the amount of displacement of each operation lever
with respect to the neutral position. The structures of the components
other than the hull ECU 104 in the marine vessel propulsion system
according to the second preferred embodiment are substantially the same
as those in the above-described first preferred embodiment, so that
descriptions of the structures of the components other than the hull ECU
will be omitted.

[0098]In the second preferred embodiment, as shown in FIG. 14, the
steering angles of the outboard motors 300 are changed based on one of
the patterns (A1), (A2), (B1), (B2), (C1), and (C2), as is the case in
the first preferred embodiment. It will be appreciated that two or more
of the patterns (A1), (A2), (B1), (B2), (C1), and (C2) in FIG. 14 may be
combined arbitrarily and used sequentially in actual marine vessel
maneuvering.

[0099]In the second preferred embodiment, the amount of change in the
steering angle of each outboard motor 300 is changed according to the
amount of displacement of each operation lever with respect to the
neutral position (i.e., throttle opening degree command).

[0100]For example, in the pattern (A1), the right and left operation
levers 102a and 102b are, respectively, in the neutral and forward drive
positions. In the pattern (A1), the steering angle of the left outboard
motor 302 is changed according to the amount of displacement of the left
operation lever 102b. As shown in FIG. 13, if the amount of displacement
of the left operation lever 102b is small (i.e., the throttle opening
degree of the left outboard motor 302 is small), the amount of change A1
in the steering angle of the left outboard motor 302 is also small. On
the contrary, if the amount of displacement of the left operation lever
102b is large (i.e., the throttle opening degree of the left outboard
motor 302 is large), the amount of change θ2 in the steering angle
of the left outboard motor 302 is also large.

[0101]In the pattern (C1), the right and left operation levers 102a and
102b are, respectively, in the reverse and forward drive positions. In
the pattern (C1), the steering angles of the right and left outboard
motors 301 and 302 are changed according to the amounts of displacement
of the respective right and left operation levers 102a and 102b. As shown
in FIG. 13, if the amounts of displacement of the right and left
operation levers 102a and 102b are small, the amounts of change θ3
in the steering angles of the right and left outboard motors 301 and 302
are also small. On the contrary, if the amounts of displacement of the
right and left operation levers 102a and 102b are large, the amounts of
change θ4 in the steering angles of the right and left outboard
motors 301 and 302 are also large.

[0102]In the second preferred embodiment, the amount of displacement of
each operation lever (i.e., throttle opening degree command) is
proportional to the amount of change in the steering angle of each
outboard motor 300. Specifically, as shown in FIG. 15, the steering angle
of each outboard motor 300 changes from, for example, about 2 degrees to
about 10 degrees (about 2 or more but about 10 or less degrees or about
-10 or more but about -2 or less degrees) while the throttle opening
degree changes from 0 to 100% (0 or more but 100 or less %).

[0103]Thus, in the second preferred embodiment, the amount of change in
the steering angle of each outboard motor 300 is changed according to the
amount of displacement of each operation lever with respect to the
neutral position (i.e., throttle opening degree command). With this
arrangement, the amount of change in the steering angle of each outboard
motor 300 can be increased by increasing the amount of operation of each
operation lever. This allows a turning or pivoting force to act more
forcefully on the hull 100 when the amount of operation of each operation
lever is increased. This allows the hull 100 to have a smaller turning
radius and it is also possible to change the behavior of the hull 100
more quickly and highly responsively.

[0104]Other advantages of the second preferred embodiment are
substantially the same as those of the above-described first preferred
embodiment.

Third Preferred Embodiment

[0105]A third preferred embodiment of the present invention will be
described with reference to FIGS. 16 and 17. In the third preferred
embodiment, the hull 100 moves laterally when the right and left
operation levers 102a and 102b are, respectively, in the forward and
reverse drive positions. The structures of the components other than the
hull ECU in the marine vessel propulsion system according to the third
preferred embodiment are substantially the same as those in the
above-described first preferred embodiment, so that descriptions of the
structures of the components other than the hull ECU will be omitted.

[0106]In the third preferred embodiment, as shown in FIG. 17, when one of
the right and left operation levers 102a and 102b is in the neutral
position, the steering angles of the outboard motors 300 are changed
based on one of the patterns (A1), (A2), (B1), and (B2), as is the case
in the first preferred embodiment. However, when the right and left
operation levers 102a and 102b are, respectively, in the forward and
reverse drive positions, the steering angles of the outboard motors 300
are controlled such that the hull 100 moves laterally, unlike the first
preferred embodiment.

[0107]For example, as shown in FIG. 16 and indicated by (E1) in FIG. 17,
when the right and left operation levers 102a and 102b are, respectively,
in the reverse and forward drive positions, the steering angle of the
right outboard motor 301 is changed to be about +10 degrees and the
steering angle of the left outboard motor 302 is changed to be about -10
degrees, for example. Similarly, as indicated by (E2) in FIG. 17, also
when the right and left operation levers 102a and 102b are, respectively,
in the forward and reverse drive positions, the steering angle of the
right outboard motor 301 is changed to be about +10 degrees and the
steering angle of the left outboard motor 302 is changed to be about -10
degrees, for example. That is, when the positional combination of the
right and left operation levers 102a and 102b includes the forward and
reverse drive positions, the steering angles of the right and left
outboard motors 301 and 302 are changed such that the rear end portions
of the right and left outboard motors 301 and 302 are moved away from
each other. In this case, the propulsive force vectors of the right and
left outboard motors 301 and 302 are both directed to the rotational
center of the hull 100. This causes the hull 100 to move laterally with
little pivoting. More specifically, in the pattern (E1) shown in FIG. 16,
the resultant force of the propulsive forces of the right and left
outboard motors 301 and 302 causes the hull 100 to move rightward.
Similarly, in the pattern (E2) shown in FIG. 17, the resultant force of
the propulsive forces of the right and left outboard motors 301 and 302
causes the hull 100 to move leftward.

[0108]In the third preferred embodiment, the lateral movement speed of the
hull 100 can be changed by changing the amount of displacement of each
operation lever, as shown in FIGS. 18 and 19. That is, if the amount of
displacement of each operation lever is small, the propulsive force of
the corresponding outboard motor 300 (right outboard motor 301 and left
outboard motor 302) is also small to result in a lower movement speed. On
the contrary, if the amount of displacement of each operation lever is
large, the propulsive force of the corresponding outboard motor 300
(right outboard motor 301 and left outboard motor 302) is also large to
result in a higher movement speed.

[0109]Thus, in the third preferred embodiment, the hull 100 can move
laterally with the propulsive forces of the right and left outboard
motors 301 and 302 without using a side thruster.

[0110]Other advantages of the third preferred embodiment are substantially
the same as those of the above-described first preferred embodiment.

Fourth Preferred Embodiment

[0111]A fourth preferred embodiment of the present invention will be
described with reference to FIG. 20. In the fourth preferred embodiment,
the hull 100 moves laterally when the positional combination of the right
and left operation levers 102a and 102b includes the forward and reverse
drive positions, unlike the first preferred embodiment. The structures of
the components other than the hull ECU 104 in the marine vessel
propulsion system according to the fourth preferred embodiment are
substantially the same as those in the above-described first preferred
embodiment, so that descriptions of the structures of the components
other than the hull ECU will be omitted.

[0112]In the fourth preferred embodiment, as shown in FIG. 20, the
steering angles of the outboard motors 300 are changed based on one of
the patterns (A1), (A2), (B1), (B2), (E1), and (E2), as is the case in
the third preferred embodiment. In the fourth preferred embodiment, the
amount of change in the steering angle of each outboard motor 300 is
changed according to the amount of displacement of each operation lever
in the patterns (A1), (A2), (B1), and (B2). That is, in the fourth
preferred embodiment, the control according to the second preferred
embodiment is performed in the patterns (A1), (A2), (B1), and (B2), while
the lateral movement control according to the third preferred embodiment
is performed in the patterns (E1) and (E2).

[0113]Advantages of the fourth preferred embodiment are substantially the
same as those of the above-described first to third preferred
embodiments.

Fifth Preferred Embodiment

[0114]A fifth preferred embodiment of the present invention will be
described with reference to FIGS. 21 and 21A. The fifth preferred
embodiment describes the case where three outboard motors are mounted on
the hull 100, unlike the above-described first preferred embodiment in
which two outboard motors are mounted on the hull 100. In FIG. 21A,
components identical to those in FIG. 3 are designated by the same
reference numerals.

[0115]In the fifth preferred embodiment, three outboard motors (right
outboard motor 501, center outboard motor 502, and left outboard motor
503) are mounted on the hull 100, respectively, via three steering units
201, 202, and 203. The steering units 201, 202, and 203 include,
respectively, motors 201a, 202a, and 203a, actual rudder angle sensors
201b, 202b, and 203b, and steering ECUs 201c, 202c, and 203c. The
steering ECUs 201c, 202c, and 203c are arranged to be capable of
communicating information with the hull ECU 104 through the LAN 10. The
outboard motors 501, 502, and 503 each include a motor 303a arranged to
drive a throttle valve, a motor 305a arranged to drive a forward-reverse
switching mechanism, and an outboard motor ECU 308. The outboard motor
ECUs 308 are arranged to be capable of communicating information with the
hull ECU 104 via the LAN 10.

[0116]The shift state and throttle opening degree of the right outboard
motor 501 are controlled correspondingly to the position of the right
operation lever 102a. The shift state and throttle opening degree of the
left outboard motor 503 are also controlled correspondingly to the
position of the left operation lever 102b. The shift state and throttle
opening degree of the center outboard motor 502 are controlled based on
the positions of the right and left operation levers 102a and 102b. The
hull ECU 104 is arranged, in the assisted marine vessel maneuvering mode,
to control the shift states, throttle opening degrees, and steering
angles of the three outboard motors based on detection results from the
two lever position sensors. In the fifth preferred embodiment, the
steering angles of the outboard motors (right outboard motor 501, center
outboard motor 502, and left outboard motor 503) are changed to drive the
behavior of the hull 100 using substantially the same patterns as in the
above-described first preferred embodiment.

[0117]For example, as shown in (Fa) and (Fb) of FIG. 21, when the right
and left operation levers 102a and 102b are, respectively, in the neutral
and forward drive positions, the steering angle of the left outboard
motor 503 that generates a propulsive force is changed to be about +10
degrees, for example, so as to follow the right-forward turning direction
of the hull 100. Since the right outboard motor 501 generates no
propulsive force, the steering angle thereof is kept at 0 degrees. Here,
when the right and left operation levers 102a and 102b are, respectively,
in the neutral and forward drive positions, the shift state of the center
outboard motor 502 may be controlled in the neutral or forward drive
state. If the shift state of the center outboard motor 502 is in the
neutral state as shown in (Fa) of FIG. 21, the center outboard motor 502
generates no propulsive force. Therefore, the steering angle of the
center outboard motor 502 remains unchanged at 0 degrees. If the shift
state of the center outboard motor 502 is in the forward drive state as
shown in (Fb) of FIG. 21, the center outboard motor 502 also generates a
propulsive force. Therefore, the steering angle of the center outboard
motor 502 is also changed to be about +10 degrees, for example, so as to
follow the right-forward turning direction of the hull 100.

[0118]As shown in (Ga) and (Gb) of FIG. 21, when the right and left
operation levers 102a and 102b are, respectively, in the neutral and
reverse drive positions, the steering angle of the left outboard motor
503 that generates a propulsive force is changed to be about +10 degrees,
for example, so as to follow the right-backward turning direction of the
hull 100. Since the right outboard motor 501 generates no propulsive
force, the steering angle thereof is kept at 0 degrees. Also, in this
case, if the shift state of the center outboard motor 502 is in the
neutral state as shown in (Ga) of FIG. 21, the center outboard motor 502
generates no propulsive force. Therefore, the steering angle of the
center outboard motor 502 remains unchanged at 0 degrees. If the shift
state of the center outboard motor 502 is in the reverse drive state as
shown in (Gb) of FIG. 21, the center outboard motor 502 also generates a
propulsive force. Therefore, the steering angle of the center outboard
motor 502 is also changed to be about +10 degrees so as to follow the
right-backward turning direction of the hull 100.

[0119]Similarly, when the right and left operation levers 102a and 102b
are, respectively, in the forward drive and neutral positions, the
steering angle of the right outboard motor 501 that generates a
propulsive force is changed to be about -10 degrees so as to follow the
left-forward turning direction of the hull 100. Since the left outboard
motor 503 generates no propulsive force, the steering angle thereof is
kept at 0 degrees. Here, when the right and left operation levers 102a
and 102b are, respectively, in the forward drive and neutral positions,
the shift state of the center outboard motor 502 may be controlled in the
neutral or forward drive state. If the shift state of the center outboard
motor 502 is in the neutral state, the center outboard motor 502
generates no propulsive force. Therefore, the steering angle of the
center outboard motor 502 remains unchanged at 0 degrees. If the shift
state of the center outboard motor 502 is in the forward drive state, the
center outboard motor 502 also generates a propulsive force. Therefore,
the steering angle of the center outboard motor 502 is also changed to be
about -10 degrees, for example, so as to follow the left-forward turning
direction of the hull 100.

[0120]When the right and left operation levers 102a and 102b are,
respectively, in the reverse drive and neutral positions, the steering
angle of the right outboard motor 501 that generates a propulsive force
is changed to be about -10 degrees, for example, so as to follow the
left-backward turning direction of the hull 100. Since the left outboard
motor 503 generates no propulsive force, the steering angle thereof is
kept at 0 degrees. Also in this case, if the shift state of the center
outboard motor 502 is in the neutral state, the center outboard motor 502
generates no propulsive force. Therefore, the steering angle of the
center outboard motor 502 remains unchanged at 0 degrees. If the shift
state of the center outboard motor 502 is in the reverse drive state, the
center outboard motor 502 also generates a propulsive force. Therefore,
the steering angle of the center outboard motor 502 is also changed to be
about -10 degrees, for example, so as to follow the left-backward turning
direction of the hull 100.

[0121]Further, as shown in (H) of FIG. 21, when the right and left
operation levers 102a and 102b are, respectively, in the reverse and
forward drive positions, the steering angles of the right and left
outboard motors 501 and 503 that each generate a propulsive force are
changed, respectively, to be about -10 and about +10 degrees so as to
follow the rightward pivoting direction of the hull 100. Similarly, when
the right and left operation levers 102a and 102b are, respectively, in
the forward and reverse drive positions, the steering angles of the right
and left outboard motors 501 and 503 that each generate a propulsive
force are changed, respectively, to be about -10 and about +10 degrees so
as to follow the leftward pivoting direction of the hull 100. That is, in
both of the cases above, the steering angles of the right and left
outboard motors 501 and 503 are changed such that the rear end portions
of the right and left outboard motors 501 and 503 are brought close to
each other.

[0122]It is noted that the right and left outboard motors 501 and 503 are,
respectively, examples of "first propulsion device group" and "second
propulsion device group" according to a preferred embodiment of the
present invention. The center outboard motor 502 is an example of a
"first propulsion device group" according to a preferred embodiment of
the present invention if the steering angle thereof is changed together
with the right outboard motor 501, while an example of a "second
propulsion device group" according to a preferred embodiment of the
present invention if the steering angle thereof is changed together with
the left outboard motor 503.

[0123]Advantages of the fifth preferred embodiment are substantially the
same as those of the above-described first preferred embodiment.

Sixth Preferred Embodiment

[0124]A sixth preferred embodiment of the present invention will be
described with reference to FIGS. 22 and 22A. In the sixth preferred
embodiment, three outboard motors are controlled based on the operations
of three operation levers, unlike the above-described fifth preferred
embodiment. In FIG. 22A, components identical to those in FIG. 21A are
designated by the same reference numerals.

[0125]In the sixth preferred embodiment, three operation levers 600 (right
operation lever 600a, center operation lever 600b, and left operation
lever 600c) are provided correspondingly to the three outboard motors
(right outboard motor 501, center outboard motor 502, and left outboard
motor 503) as shown in FIG. 22. Three lever position sensors 601a, 601b,
and 601c are also provided correspondingly to the three operation levers,
and output signals from these sensors are fed into the hull ECU 104.

[0126]The shift states and throttle opening degrees of the respective
right, center, and left outboard motors 501, 502, and 503 are controlled
correspondingly to the positions of the respective right, center, and
left operation levers 600a, 600b, and 600c. The hull ECU 104 is arranged,
in the assisted marine vessel maneuvering mode, to control the shift
states, throttle opening degrees, and steering angles of the three
outboard motors based on detection results from the three lever position
sensors 601a, 601b, and 601c. Also, in the sixth preferred embodiment,
the steering angles of the outboard motors are changed to facilitate the
behavior of the hull 100 using substantially the same patterns as in the
above-described first and fifth preferred embodiments.

[0127]For example, as shown in (Ia) of FIG. 22, when the right, center,
and left operation levers 600a, 600b, and 600c are, respectively, in the
neutral, neutral, and forward drive positions, only the left outboard
motor 503 generates a propulsive force. Therefore, the steering angle of
the left outboard motor 503 is only changed to be about +10 degrees, for
example, so as to follow the right-forward turning direction of the hull
100. The steering angles of the right and center outboard motors 501 and
502 are kept at 0 degrees. Also, as shown in (Ib) of FIG. 22, when the
right, center, and left operation levers 600a, 600b, and 600c are,
respectively, in the neutral, forward drive, and forward drive positions,
the center outboard motor 502 also generates a propulsive force.
Therefore, the steering angles of the left and center outboard motors 503
and 502 are changed to be about +10 degrees, for example, so as to follow
the right-forward turning direction of the hull 100. The steering angle
of the right outboard motor 501 is kept at 0 degrees.

[0128]As shown in (Ja) of FIG. 22, when the right, center, and left
operation levers 600a, 600b, and 600c are, respectively, in the neutral,
neutral, and reverse drive positions, only the left outboard motor 503
generates a propulsive force. Therefore, the steering angle of the left
outboard motor 503 is only changed to be about +10 degrees, for example,
so as to follow the right-backward turning direction of the hull 100. The
steering angles of the right and center outboard motors 501 and 502 are
kept at 0 degrees. Also, as shown in (Jb) of FIG. 22, when the right,
center, and left operation levers 600a, 600b, and 600c are, respectively,
in the neutral, reverse drive, and reverse drive positions, not only the
left outboard motor 503 but also the center outboard motor 502 generates
a propulsive force. Therefore, the steering angles of the center and left
outboard motors 502 and 503 are changed to be about +10 degrees, for
example, so as to follow the right-backward turning direction of the hull
100. The steering angle of the right outboard motor 501 is kept at 0
degrees.

[0129]Similarly, when the right, center, and left operation levers 600a,
600b, and 600c are, respectively, in the forward drive, neutral, and
neutral positions, only the right outboard motor 501 generates a
propulsive force. Therefore, the steering angle of the right outboard
motor 501 is only changed to be about -10 degrees, for example, so as to
follow the left-forward turning direction of the hull 100. The steering
angles of the left and center outboard motors 503 and 502 are kept at 0
degrees. Also, when the right, center, and left operation levers 600a,
600b, and 600c are, respectively, in the forward drive, forward drive,
and neutral positions, the center outboard motor 502 also generates a
propulsive force. Therefore, the steering angles of the right and center
outboard motors 501 and 502 are changed to be about -10 degrees, for
example, so as to follow the left-forward turning direction of the hull
100. The steering angle of the left outboard motor 503 is kept at 0
degrees.

[0130]When the right, center, and left operation levers 600a, 600b, and
600c are, respectively, in the reverse drive, neutral, and neutral
positions, only the right outboard motor 501 generates a propulsive
force. Therefore, the steering angle of the right outboard motor 501 is
only changed to be about -10 degrees, for example, so as to follow the
left-backward turning direction of the hull 100. The steering angles of
the left and center outboard motors 503 and 502 are kept at 0 degrees.
Also, when the right, center, and left operation levers 600a, 600b, and
600c are, respectively, in the reverse drive, reverse drive, and neutral
positions, not only the right outboard motor 501 but also the center
outboard motor 502 generates a propulsive force. Therefore, the steering
angles of the right and center outboard motors 501 and 502 are changed to
be about -10 degrees, for example, so as to follow the left-backward
turning direction of the hull 100. The steering angle of the left
outboard motor 503 is kept at 0 degrees.

[0131](Ka) of FIG. 22 represents the case where the right, center, and
left operation levers 600a, 600b, and 600c are, respectively, in the
reverse drive, neutral, and forward drive positions. In this case, the
steering angles of the right and left outboard motors 501 and 503 are
changed, respectively, to be about -10 and about +10 degrees, for
example, so as to follow the rightward pivoting direction of the hull
100. That is, the steering angles of the right and left outboard motors
501 and 503 are changed such that the rear end portions of the right and
left outboard motors 501 and 503 are brought close to each other. The
steering angle of the center outboard motor 502 remains unchanged at 0
degrees.

[0132]The same applies to the case where the right, center, and left
operation levers 600a, 600b, and 600c are, respectively, in the forward
drive, neutral, and reverse drive positions. In this case, the steering
angles of the right and left outboard motors 501 and 503 are changed,
respectively, to be about -10 and about +10 degrees, for example, so as
to follow the leftward pivoting direction of the hull 100. That is, the
steering angles of the right and left outboard motors 501 and 503 are
changed such that the rear end portions of the right and left outboard
motors 501 and 503 are brought close to each other. The steering angle of
the center outboard motor 502 remains unchanged at 0 degrees.

[0133]Also, (Kb) of FIG. 22 represents the case where the right, center,
and left operation levers 600a, 600b, and 600c are, respectively, in the
reverse drive, forward drive, and forward drive positions. In this case,
the steering angles of the right, center, and left outboard motors 501,
502, and 503 are changed, respectively, to be about -10, about +10, and
about +10 degrees, for example, so as to follow the rightward pivoting
direction of the hull 100. That is, the steering angles of the right,
center, and left outboard motors 501, 502, and 503 are changed such that
the rear end portion of the right outboard motor 501 and the rear end
portions of the left as well as center outboard motors 503 and 502 are
brought close to each other.

[0134]The same applies to the case where the right, center, and left
operation levers 600a, 600b, and 600c are, respectively, in the forward
drive, forward drive, and reverse drive positions. In this case, the
steering angles of the right, center, and left outboard motors 501, 502,
and 503 are changed, respectively, to be about -10, about -10, and about
+10 degrees, for example, so as to follow the leftward pivoting direction
of the hull 100. That is, the steering angles of the right, center, and
left outboard motors 501, 502, and 503 are changed such that the rear end
portions of the right as well as center outboard motors 501 and 502 and
the rear end portion of the left outboard motor 503 are brought close to
each other.

[0135]When the right, center, and left operation levers 600a, 600b, and
600c are, respectively, in the reverse drive, reverse drive, and forward
drive positions, the following operation will occur. That is, the
steering angles of the right, center, and left outboard motors 501, 502,
and 503 are changed, respectively, to be about -10, about -10, and about
+10 degrees, for example, so as to follow the rightward pivoting
direction of the hull 100. In this case, the steering angles of the
right, center, and left outboard motors 501, 502, and 503 are changed
such that the rear end portions of the right as well as center outboard
motors 501 and 502 and the rear end portion of the left outboard motor
503 are brought close to each other.

[0136]The same applies to the case where the right, center, and left
operation levers 600a, 600b, and 600c are, respectively, in the forward
drive, reverse drive, and reverse drive positions. That is, the steering
angles of the right, center, and left outboard motors 501, 502, and 503
are changed, respectively, to be about -10, about +10, and about +10
degrees, for example, so as to follow the leftward pivoting direction of
the hull 100. In this case, the steering angles of the right, center, and
left outboard motors 501, 502, and 503 are changed such that the rear end
portion of the right outboard motor 501 and the rear end portions of the
left as well as center outboard motors 503 and 502 are brought close to
each other.

[0137]The right and left operation levers 600a and 600c are, respectively,
examples of "first operation lever" and "second operation lever"
according to a preferred embodiment of the present invention. The center
operation lever 600b is an example of a "first operation lever" according
to a preferred embodiment of the present invention if in the same
position as the right operation lever 600a, while an example of a "second
operation lever" according to a preferred embodiment of the present
invention if in the same position as the left operation lever 600c.

[0138]Advantages of the sixth preferred embodiment are substantially the
same as those of the above-described first preferred embodiment.

Other Preferred Embodiments

[0139]The above-disclosed preferred embodiments of the present invention
are to be considered in all aspects only as illustrative and not
restrictive. The scope of the present invention is not defined by the
above-described preferred embodiments, but rather by the claims appended
hereto. Further, the present invention includes all the modifications
within the meaning and scope equivalent to those defined by the appended
claims.

[0140]For example, although the first to sixth preferred embodiments above
describe the case where two or three operation levers are preferably used
to steer two or three outboard motors, the present invention is not
restricted thereto. Two or more operation levers may be used to steer
four or more outboard motors, including the case, for example, where two
operation levers are used to steer four outboard motors.

[0141]Although the first to sixth preferred embodiments above describe the
case where outboard motors that generate a propulsive force by rotating a
propeller with a driving force from an engine are preferably adopted, the
present invention is not restricted thereto. That is, outboard motors and
other propulsion devices may be adopted that generate a propulsive force
by rotating a propeller with a driving force from an electric motor. Not
only propulsion devices that generate a propulsive force by rotating a
propeller but also propulsion devices (jet propulsion devices) that
generate a propulsive force through jet drive in which water is jetted
through an injection nozzle may be adopted.

[0142]Although the first to sixth preferred embodiments above describe the
case where a marine vessel maneuvering operator preferably operates the
selector switch to switch between the normal marine vessel maneuvering
mode and the assisted marine vessel maneuvering mode, the present
invention is not restricted thereto. That is, it may be arranged that the
normal marine vessel maneuvering mode switches automatically to the
assisted marine vessel maneuvering mode if predetermined conditions are
met.

[0143]Although the first to sixth preferred embodiments above describe the
case where the normal marine vessel maneuvering mode is preferably
switchable to one assisted marine vessel maneuvering mode, the present
invention is not restricted thereto. For example, it may be arranged that
the operator can select from among multiple assisted marine vessel
maneuvering modes. The multiple assisted marine vessel maneuvering modes
may include any two or more modes described in the first to sixth
preferred embodiments.

[0144]Although the first preferred embodiment above describes the case
where the amount of change in the steering angle of each outboard motor
is preferably fixed to about 10 degrees, for example, the present
invention is not restricted thereto. The steering angle may be changed to
a value other than approximately 10 degrees.

[0145]Although the first preferred embodiment above describes the case
where the amount of change in the steering angle of the right outboard
motor and the amount of change in the steering angle of the left outboard
motor are preferably both set to the same angle (e.g., about 10 degrees),
the present invention is not restricted thereto. That is, the amount of
change in the steering angle of the right outboard motor may be different
from the amount of change in the steering angle of the left outboard
motor.

[0146]Although the first preferred embodiment above describes the case
where the steering angle of each outboard motor is preferably changed
when the shift state corresponding to the position of the right operation
lever 102a is different from the shift state corresponding to the
position of the left operation lever 102b, the present invention is not
restricted thereto. For example, even if the shift state corresponding to
the position of the right operation lever 102a may be the same as the
shift state corresponding to the position of the left operation lever
102b (e.g., both in the forward drive position), the steering angle of
each outboard motor may be changed from its neutral position when the
right and left operation levers 102a and 102b are in their respective
different positions (i.e., the throttle opening degree commands for the
right and left outboard motors are different from each other).

[0147]Although the second preferred embodiment above describes the case
where the amount of displacement of each operation lever is preferably
proportional to the amount of change in the steering angle of each
outboard motor, the present invention is not restricted thereto. The
relationship therebetween may not be a proportional one.

[0148]Although the first preferred embodiment above describes the case
where the throttle opening degree is preferably controlled such that the
relationship between the amount of displacement of each operation lever
and the throttle opening degree in the assisted marine vessel maneuvering
mode is the same as in the normal marine vessel maneuvering mode, the
present invention is not restricted thereto. That is, in the assisted
marine vessel maneuvering mode, the throttle opening degree may be
controlled to be smaller than in the normal marine vessel maneuvering
mode. For example, as shown in FIG. 23, the throttle opening degree may
be controlled according to the characteristics in that the throttle
opening degree at the maximum amount of displacement of each operation
lever is approximately 30% of the maximum throttle opening degree in the
normal marine vessel maneuvering mode, for example. Alternatively, an
upper limit may preliminarily be set on the engine speed, and in the
assisted marine vessel maneuvering mode, the throttle opening degree may
be controlled such that the engine speed does not exceed the upper limit.

[0149]While preferred embodiments of the present invention have been
described above, it is to be understood that variations and modifications
will be apparent to those skilled in the art without departing the scope
and spirit of the present invention. The scope of the present invention,
therefore, is to be determined solely by the following claims.

[0150]The present application corresponds to Japanese Patent Application
No. 2009-014987 filed in the Japan Patent Office on Jan. 27, 2009, and
the entire disclosure of the application is incorporated herein by
reference.